This invention relates to a deflection yoke for a cathode ray tube.
Generally, a deflection yoke includes a pair of vertical deflection coils, a pair of horizontal deflection coils, a truncated cone made of magnetic material for enhancing a flux created by the coils and a separator or liner. The two pairs of deflection coils are separated from each other by the separator, generally made of plastic. The separator enhances the mechanical stiffness and fixes the coils with respect to one another. The separator includes a main body in the shape of a funnel and a flexible rear part adapted to surround the tube neck for attaching the deflection yoke onto the tube neck to establish the longitudinal position of the yoke. This attachment is generally made using a clamp collar placed around the rear flexible part.
In a saddle-saddle (S--S) yoke, the horizontal deflection coils are placed around an inside wall of the separator and are generally held in place by clipping and/or gluing. The vertical deflection coils are placed around an outside wall of the separator. The front part of the vertical deflection yoke may be attached by inserting it in a housing provided on the separator. The ring shaped core made of ferromagnetic material is placed around the vertical deflection coils and partially covers them.
The rear part of the vertical deflection coils is held in place so that the position of the core can be adjusted to provide convergence. After this adjustment has been made, the core is permanently attached. FIG. 1 illustrates a prior art deflection yoke 1 that includes a pair of saddle-shaped horizontal deflection coils 3, a pair of vertical deflection coils 4, also saddle-shaped, separated from horizontal deflection coils 3 by a separator 2. A core 5 made of magnetic material is placed around coils 3 and 4. Deflection yoke 1 is placed on a neck 8 of a cathode ray tube (CRT) 6 in order to provide deflection of electron beams from an electron gun 7. Consequently, a raster can be formed on a screen surface 9. The various elements used in yoke 1 can be held in an optimum adjustment position by gluing. Thus, separator 2 supports the various elements and provides the mechanical stiffness of the assembly. However, disadvantageously, support by gluing slows down the manufacturing process. This is so because core 5 can be positioned only after coils 4 have been permanently fixed in place. Moreover, supporting the rear part of coils 4 by gluing may not be reliable due to mechanical stresses applied to yoke 1 during adjustment when yoke 1 is placed on the tube neck.
Another prior art construction method is shown in FIG. 2. Similar symbols in FIGS. 1 and 2 indicate similar items or functions. In the yoke of FIG. 2, the vertical deflection coils and the core are held in position by means of a ring 13 that attaches onto rails 10 placed on a cylindrical part of separator 2. An elastic split ring 14 is used to attach the deflection yoke of FIG. 2 onto the tube neck using a clamping collar, not shown, placed around ring 14. Ring 13 slides on rails 10 until the vertical deflection coils, not shown, come into contact with the front of the separator. Ring 13 is glued for permanent attachment of the assembly. Ring 13 may be used for assembling torroidal type vertical deflection coils that are wound around a core made of magnetic material. In such a case, ring 13 mechanically supports both the vertical deflection coils and the core.
For saddle-shaped coils, such as shown in FIG. 1, coils 4 extends along the Z-axis over a length greater than the length of core 5. Thus, an arrangement such as shown in FIG. 2 may not be able to mechanically support core 5.